The present invention relates to novel high performance polymer compositions that can be utilized for microelectronic packaging.
Fluorine-containing polymeric materials are used in a variety of space and aerospace applications. Although the costs of such materials are high, they have the desirable characteristic of lowering the dielectric constant of a polymeric system. Low dielectric properties of a material are of particular importance in the area of microelectronic packaging. Interconnect processing of functional devices on the silicon chip will soon require insulators with dielectric constants from 2.0-2.4. These materials must also exhibit Tg""s between 350-400xc2x0 C., excellent thermo-oxidative stability, and low moisture uptake to be compatible with lead-bath processing.
In U.S. Pat. No. 6,057,417, issued May 2, 2000 to Fred E. Arnold, et al, there is disclosed a polymer system having repeating units of the formula: 
wherein A is xe2x80x94H or xe2x80x94OH, x has a value of 0.5 to 1.0 and y has a value of 1.0-x. These polymers meet the requirements set forth above.
We have now discovered that these and other benzazole polymers and copolymers containing the 2-hydroxy-p-phenylene moiety can be made crosslinkable.
Accordingly, it is an object of the present invention to provide crosslinkable benzazole polymers and copolymers.
Other objects, aspects and advantages of the present invention will be apparent to those skilled in the art from a reading of the following detailed disclosure of the invention.
In accordance with the invention there is provided an oxyallyl pendent polymer system having repeating units of the formulae
hereinafter referred to as structure A, wherein x has a value of about 0.1 to 1.0 and y has a value of 1.0-x, and
hereinafter referred to as structure B, wherein the sum of p+q has a value of about 0.1 to 1.0, r has a value of 1.0-(p+q) and the molar ratio of p:q is about 9:1 to 1:9, wherein Bz is a benzazole unit selected from the group consisting of
wherein X is xe2x80x94O, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94, and R is selected from the group consisting of
and wherein Ar is an aromatic group.
The polymers and copolymers of this invention are derived from polymers and copolymers containing the 2-hydroxy-p-phenylene moiety. The incorporated 2-hydroxy-p-phenylene repeat unit allows for post-polymer reactions to provide oxyallyl pendent groups which can be used to cure or crosslink the polymer/copolymer units.
The derivitizable polymers and copolymers are prepared by the condensation of 2-hydroxyterephthalic acid, a benzazole precursor such as 
wherein R and X are as defined previously, and, optionally, an aromatic dicarboxylic acid (HOOCxe2x80x94Arxe2x80x94COOH), in polyphosphoric acid (PPA) at about 180xc2x0 C., following procedures well known in the art, then recovered, also using procedures well known in the art.
The 2-hydroxy-p-phenylene-containing homo- and copolymer compositions are then derivatized utilizing the hydroxy proton. Derivatization of these compositions is carried out by treatment with excess potassium carbonate in dimethylformamide (DMF) to form the hydroxy potassium salt. The polymeric salt is then reacted with allylbromide to form the new oxyallyl composition. Structure A, above, results when excess allylbromide is used; structure B results when the quantity of allylbromide is limited to less than a stoichiometric amount, thereby limiting the degree of crosslinking in the later cured polymer. The resulting derivatized polymer/copolymer is recovered by precipitation into water, followed by soxhlet extraction with heptane to remove unreacted allylbromide. Alternatively, derivitization can be carried out with sodium hydride in dimethylsulfoxide (DMSO).
The pendent allyl polymer/copolymer can be crosslinked by heating or by using the appropriate free radical-initiating reagents. As shown in the Examples which follow, the polymer/copolymer exhibits two exotherms, the first about 220xc2x0 to 250xc2x0 C., and the second about 385xc2x0 to 400xc2x0 C. Accordingly, the polymer/copolymer can be crosslinked by heating to a temperature in the range of the first exotherm for a relatively short time, about 30 sec to 5 minutes, followed thereafter by heating to a temperature in the range of the second exotherm, again for a relatively short time. Alternatively, the polymer/copolymer can be crosslinked by heating to a temperature of about 260xc2x0 C. in an inert atmosphere for about 30-120 minutes.